The present invention is directed to an aqueous sizing composition for treating glass fibers and a process for making sized glass fiber strands. More particularly, the present invention is related to a sizing composition useful in sizing glass fibers so as to improve the process of formation of precision wound packages of glass fiber strands for use in polymeric reinforcement.
Sizing compositions are used in producing glass fibers in order to protect the glass fiber strand in subsequent processing and, where the glass fibers are to be used in plastic reinforcement, to provide adhesion between the glass fibers and the polymer matrix. The sizing composition is generally applied to the glass fiber strands after the multitude of fine glass filaments that are combined to make up the strand are formed by the rapid attenuation from molten cones of glass at the tips of small orifices in a bushing. After the filaments have been treated with the sizing composition and gathered together into a strand or strands, the glass fiber strand is wound around a rapidly rotating drum to form the package.
For use in the reinforcement of polymer matrices the sized and wound glass fiber strands can be made into roving, chopped strand or mat. Roving is formed by mounting a plurality of glass fiber forming packages on a creel or support and gathering the strands from the separate packages in parallel, to form a rope or roving. This braided rope or roving is wound on a rotating drum to collect the roving. The roving so produced has a plurality of uses. It cain be chopped and separated to form separated chopped strand, or it can be woven to form woven roving, or it can be used by merely unwinding and impregnating the roving with resin for applications such as filament winding and pultrusion. In order to obtain a glass fiber roving which is useful for reinforcement, it is desirable that the formation and processing of the roving must present as few problems as possible in production. In this regard it was recently suggested in U.S. Pat. No. 3,997,306 (Hedden) to use a sizing composition in the formation of glass fiber strand to be used in polymer reinforcement that could be used in many types of polymers such as epoxy, polyester, and vinyl ester resin matrices.
The sizing composition of U.S. Pat. No. 3,997,306 (Hedden) comprises a phenolic epoxy resin, the reaction product of a partial ester of a polycarboxylic acid, which contained one or more unesterified carboxyl groups, with a compound containing more than one epoxy group, a glass fiber lubricant, sufficient emulsifiers or wetting agents to make a homogeneous mixture, an amino silane coupling agent and a methacryloxyalkyltrialkoxysilane coupling agent. The desired pH range for the size is between about 5.5 and 7.5 with an optimum solids concentration of 4.0 to 6.0 percent.
In addition to producing rovings from forming packages of glass fiber strand, the art has developed the method and necessary apparatus for formation of precision wound packages of glass fiber strands during the fiber forming process while the winding still provides the attenuation necessary to form the glass filament from the glass fiber bushing. The finished package is normally cylindrical in shape and should have a flat surface with flat edges on either end. The package can be one having single strand roving or one where the roving may comprise multiple strands, but in both the roving is compact at the end regions of the package thereby providing the cylindrical shape of the package.
In producing the precision wound packages of glass fiber strands and roving, the strand or roving of the packages contain considerable quantities of water, usually around 10 to 15 percent by weight, because they are wound during fiber glass forming operations wherein an aqueous sizing composition is used. The packages containing the glass fiber strand or roving with such a high quantity of water must be dried before shipment. One process for producing a precision wound package of glass fiber strand or roving, having a reduced moisture content involves the following steps. The filaments are drawn from the glass fiber forming bushing which is supplied continuously with molten glass. The drawn glass fiber filaments are treated with a suitable sizing composition from an aqueous sizing composition bath by drawing them over an applicator which places the sizing composition on the filaments. The filaments are then passed through a drying zone to reduce the moisture content to 8 percent by weight or less. The dried filaments are then gathered into a strand and the strand is wound on a winder having a horizontal traversing guide vehicle and guide eye constructed so that edge distortion is reduced in the package being wound. The precision wound packages are then removed and dried to completion in a drying oven.
It is an object of the present invention to provide a sizing composition for use with glass fibers that permits the treated glass fibers to be used as reinforcement in polymeric matrices such as epoxy, polyesters, and vinyl ester wherein the need for drying the treated glass fiber is reduced.
It is an additional object of the present invention to provide a sizing composition for treating glass fibers that are to be wound during the fiber forming process directly into precision wound packages of glass fiber strand or roving to be used in polymer reinforcement wherein the need for drying the precision wound packages is reduced.
It is another further object of the present invention to provide an improved process for producing precision wound packages of glass fibers strand or roving during the fiber forming process.
It is a further additional object of the present invention to provide a sizing composition for treating glass fibers to be used in polymer reinforcement wherein the sizing composition controls the moisture of the treated glass fiber strand.